The present invention relates to improvements to pneumatic tires of the type in which the casing has at least one sidewall ornamented with patterns in the form of a circular ring or several circular rings, or in the form of inscriptions, markings or ornaments of different kind, the said patterns being of an elastomer of a colour different from that of the sidewall which covers the carcase, so as to appear with particularly eye-catching characteristics on the black background.
The invention also relates to improvements to the manufacture of the pneumatic tires of the kind set out above.
The elastomer of a colour different from black, normally used in the art to provide patterns on the sidewalls of tires, undergoes more rapid deteriorations in time than the other parts of the tire, mainly because it is not reinforced with the lampblack filler.
In fact the said elastomer can be easily lacerated, ages rapidly and cranks to the extent that in time it fissures, developing incisions of considerable size, such as will significantly impair and compromise the efficiency of the carcase.
The said cracks and slits develop more readily and more prematurely when the carcase is of the radial type, due to the fact that such a carcase is more deformable and, therefore, the thickness of non-black elastomer is subject to greater stresses in working conditions, which do not occur in carcasses of the cross-ply type.
Hardly noticeable improvements are achieved by applying to the radial carcasses non-black elastomeric mixtures of high quality and therefore very expensive.
In the following description a non-black elastomer will be called "white" for the sake of brevity, this will be intended to signify any colour different from black.
White is in any case the most widely used colour for applying patterns to the sidewalls of tires.